Speaker
Mr
Kunihiko Tajiri
(Dep. of Phys., Osaka Univ., Osaka, Japan)
Description
The exotic structure of neutron-rich nuclei around “island of inversion” characterized by the disappearance of the neutron magic number $N$ = 20 has been attracting attention. However, most of the information on the excited states of these nuclei, such as spin and parity and so on, has not been known well. We have developed a new method to unambiguously determine the spin-parities of daughter nuclei by taking advantage of asymmetric $\beta$-ray emission in $\beta$-decay of spin-polarized unstable nuclei.
We have performed experiments using highly-polarized Na beams to systematically study the shell evolution of neutron-rich Mg isotopes. The $\beta$-ray asymmetry parameters and $\gamma$-ray intensities have successfully assigned spin-parities of levels in $^{28}$Mg and $^{29}$Mg. The level energies, log-$ft$ values and decay properties of all the assigned levels were explained well by assuming sd-shell configurations calculated by using shell model code, NuShell with USD, USDA and USDB interactions.. However, in $^{29}$Mg, two levels at 1.095 and 1.430 MeV associated with large log-$ft$ values could not be reproduced by the sd-shell configurations. The Monte Carlo Shell Model calculation shows the possibility of the states with the intruder configurations predicted 3/2$^-$ and 7/2$^-$ levels around 1 MeV. This fact strongly suggests negative-parity assignment for these two states in $^{29}$Mg. Experiment with spin-polarized $^{30}$Na beam was carried out last year and the data analysis is in progress.
Results of $^{28}$Mg and $^{29}$Mg as well as some new findings of $^{30}$Mg will be presented.
Primary author
Mr
Kunihiko Tajiri
(Dep. of Phys., Osaka Univ., Osaka, Japan)
Co-authors
A. Odahara
(Dep. of Phys., Osaka Univ.., Osaka, Japan)
A. Takashima
(Dep. of Phys., Osaka Univ.., Osaka, Japan)
C. Petrache
(Univ. of Paris Sud, France)
C.D.P. Levy
(TRIUMF, Canada)
H. Miyatake
(KEK, Ibaraki, Japan)
H. Nishibata
(Dep. of Phys., Osaka Univ.., Osaka, Japan)
J. Takatsu
(Dep. of Phys., Osaka Univ.., Osaka, Japan)
K. Kura
(Dep. of Phys., Osaka Univ.., Osaka, Japan)
M. Pearson
(TRIUMF, Canada)
M. Suga
(Dep. of Phys., Osaka Univ.., Osaka, Japan)
N. Hamatani
(Dep. of Phys., Osaka Univ.., Osaka, Japan)
N. Imai
(KEK, Ibaraki, Japan)
P. Jackson
(TRIUMF, Canada)
R. Leguillon
(Univ. of Paris Sud, France)
R. Yokoyama
(CNS, Univ. of Tokyo, Saitama, Japan)
T. Fukuchi
(RIKEN, Saitama, Japan)
T. Hori
(Dep. of Phys., Osaka Univ.., Osaka, Japan)
T. Masue
(Dep. of Phys., Osaka Univ.., Osaka, Japan)
T. Shimoda
(Dep. of Phys., Osaka Univ., Osaka, Japan)
T. Suzuki
(RCNP, Osaka Univ.., Osaka, Japan)
Y. Hirayama
(KEK, Ibaraki, Japan)
Y. Kenmoku
(Dep. of Phys., Osaka Univ.., Osaka, Japan)
